Making the most of cork

A team of researchers at the
Portuguese Amorim Group, the world's leading producer and distributor of cork products,
has developed and patented an ingenious method to dramatically expand cork's
volume without using any harmful foreign substances. The invention promises to
not only help the centuries-old cork industry thrive in the new millennium but
also supports environmentally friendly, sustainable production and ensures wine
aficionados continue to enjoy the beloved cork stopper for years to come.

The waiting game

The
satisfying pop that comes from uncorking a good bottle of merlot or chardonnay
is music to the ears of any wine connoisseur. Fine wine takes time, and so does
the cork used to seal its bottle. In fact, the cork used to make wine bottle
stoppers comes from the bark of a cork oak tree, which is only able to produce
a yield every nine to twelve years.

Producers in Portugal and Spain,
the two countries that generate the lion's share of the world's cork, have long
known the important ingredients that go into growing a perfect harvest: a warm,
dry climate with regular rainfalls, and a healthy dose of patience.

Cork
producers must first wait 25 years until a young oak has matured into a
cork-producing tree, and then about a decade between harvests to allow the oak
to regenerate its bark.

A versatile product

The
wait is worthwhile. A cork tree lives about 200 years, and its unique bark is
an important component in a variety of products. Cork, of course, floats on
water; it is quite elastic, partially permeable to air - the property that
makes it ideal as a wine stopper - but it also makes an excellent, non-toxic
insulation material because it lets through little heat or cold.

Cork is found in products as
diverse as shoe soles, cricket balls and - when treated with adhesives - floor
panels. It can even orbit the planet in the form of spacecraft heat shields.

Undoubtedly,
cork's best-known use lies in the roughly 16 billion cork bottle stoppers
produced every year and sold to the wine industry worldwide. About 80% of all
wine bottles are equipped with cork stoppers, and they offer several important
advantages over their plastic and screw-cap rivals. Not only do cork stoppers
allow oxygen to interact with wine for proper aging, their use supports an
industry with a track record of environmentally responsible and sustainable
production.

However,
the rather long interval between harvests and the limited number of cork oak
trees have put limits to the industry. Further pressure has come from plastic
stoppers and screw caps, which are cheaper to produce and have gouged out a 20%
chunk of cork's once unquestioned dominance of the wine market.

Pump up the volume

Amid
this ‘battle for the bottle', methods that can increase cork yields and further
improve the bark's expansive properties has become increasingly important.
Here, even little improvements can translate into big returns.

Since
the early 1990s, a team of Portuguese scientists has been working on solving
this issue. The team is comprised of: António Velez Marques (professor at the
Polytechnic Institute in Lisbon), Helena Pereira
(professor at the Technical University of Lisbon), Rui Reis, (CEO of the
European Institute of Excellence on Tissue Engineering and Regenerative
Medicine) and Susana Silva Estima Martins (head of the R&D department at
Corticeira Amorim).

In 1993, this research team developed a patented method of
expanding cork in an autoclave - a sterilising machine. Using this method, cork was exposed to high-pressure
saturated steam to increase its volume. However, this procedure also involved
the use of solvents such as methanol, ethanol, formic acid, dichloromethane or
chloroform.

Traces of these toxic
solvents would remain in the cork after the process, and the residual toxicity,
along with the sheer logistical feat of using an autoclave, prevented this
method from taking off in the industry.

Just put it in the
microwave

The
team continued to search for easier expansion methods that didn't require toxic
chemicals or leave undesirable residues. Through these efforts, they discovered
that cork swells when exposed to microwave radiation. Microwaves had already
been used to clean, sterilise or decontaminate cork, but its use to expand the
material's volume had not been researched.

Through
a series of tests, the team developed a new expansion process that uses only
water and microwave radiation to increase cork's volume by 40 to 85%. The
process not only increases corks elasticity and buoyancy - the very
characteristics that make it a sought-after material - it also allows
significantly more products, in this case wine stoppers, to be produced from
the same yield.

A boon for wine
drinkers

The
method patented by the Portuguese team is suitable for nearly all types of
cork: virgin cork taken directly from trees, cork that has been ground into a
powder or cut into planks, and even the small cork shavings left over from
plank and stopper production. This means that nearly every application for
which cork is used benefits from greater yields and more competitive pricing.

Especially
important for wine drinkers, the process reduces cork's already low density and
makes sure the material has the perfect level of permeation (the wine's interaction
with air) to age the finest bottles of vino.

From Portugal to worldwide locations

The
innovative new expansion method was patented in 2011 by Corticeira Amorim. The
company produces about 4 billion cork stoppers each year that are exported to
more than 100 countries.

Amorim's
3,357 employees generated sales of €295 million in 2011. The company holds 25%
share of the worldwide cork stopper market, 55% of the composite cork market,
65% of the cork floor market and 80% of the cork insulation business.

How it works

Cork has a cellular matrix
similar to a honeycomb. The cells have flexible, curved walls that surround
pockets filled with air. If these curved cell walls are straightened, the cork material
increases in volume. For this straightening to occur, the pressure of the air
inside the cells must be raised, and the cork's cell walls softened.

The
cork-expansion method invented by the Portuguese team of scientists aims for
the maximum net volume increase in the shortest amount of time while employing
a minimum amount of energy. However, because cork is insulating, heating up the
inside of the material in order to increase air pressure is no easy feat.

This
problem is solved through the exposure of cork to microwave radiation, which causes
heat to penetrate the cork quickly and thoroughly, the same way regular kitchen
microwaves heat up a meal. Because microwaves need moisture to warm materials
and cork contains very little water, it has to be moistened - either cooked in
water or steamed - before radiation is applied.

The
microwaves rapidly heat the water in the cork, which in turn heats up the cell
walls and increases the pressure inside the cells. At the same time, it pushes
the water out of the cork. The combined result of adding water and then
exposing the cork to microwave radiation causes the water to dissipate and the
cork material to expand by up to 85%.

Cork production and
the environment

The expansion method developed by the Portuguese team is a rare
example of technical innovation contributing to the protection of an age-old
traditional industry. The technology supports the survival of what is recognised
by numerous wildlife and environmental groups as an important sustainable and
eco-friendly resource.

The cork harvest employs tens of thousands
of workers each summer, so the cultivation of cork forests is an important
sector for the producer countries. And because cork oaks are not cut down
during harvest, the forests and their ecosystems are preserved, contributing to
a healthy environment, protecting valuable habitat for numerous animals and
helping combat desertification.

Cork oaks consume three to five times more
carbon dioxide than normal while they are regenerating bark, thus contributing
to the reduction of the greenhouse gases that cause climate change.